The first and only two humans to visit the Challenger Deep did so in 1960, and in recent years not a single submersible has existed that's rated for that depth.

The first and only two humans to visit the Challenger Deep did so in 1960, and in recent years not a single submersible has existed that's rated for that depth. We, as a species, have not gone back since. In contrast, twelve humans have walked on the surface of the moon. Now we're finally going back! This is so cool!